Diazotype photoprinting materials and methods of use



United States Patent 3,499,760 DIAZOTYPE PHOTOPRINTING MATERIALS AND METHODS OF USE Luigi Amariti and Hartwell L. Briggs, Chicago, 11]., as-

signors to Eugene Dietzgen Company, Chicago, Ill., a corporation of Delaware No Drawing. Continuation-impart of application Ser. No. 487,043, Sept. 13, 1965. This application May 2, 1968, Ser. No. 726,196

Int. Cl. G03c 1/58, 5/34 US. Cl. 96-49 11 Claims ABSTRACT OF THE DISCLOSURE Heat developable diazotype photoprinting compositions in which a coupler is used containing an enolate structure. The system is able to couple under the influence of heat without requiring the use of alkaline solutions or vapors or alkaline generating compounds.

This application is a continuation-impart of our copending application Ser. No. 487,043, filed Sept. 13, 1965, now abandoned.

The present invention relates to improved diazotype photoprinting materials. More particularly, the subject invention is directed to heat devlopable diazotype photoprinting compositions.

In diazotype photoprinting processes, a suitable base such as paper is treated with a solution of two dye components. One of the components is a diazo compound which is sensitive to light, and the other component is an azo coupling compound. The coupling compound is capable of reacting under proper conditions with the diazo component to form a dye. In making a print, the treated base is exposed to light under a translucent original or master. In those areas of the base which are reached by the light, the diazo compound is at least partially destroyed. In those areas that are beneath opaque lines or designs, on the other hand, the diazo compound is not affected by the light. The print is developed by reacting the retained diazo compound with the coupler to form a highly colored azo dyestuff in precise duplication of the original.

Diazotype reproduction processes are classified as either moist processes or dry processes. In a moist process the base is coated with a diazo compound which is exposed to light under a pattern. Thereafter, color development is brought about by contacting the latent diazo image with a solution of a coupling compound and aqueous alkali. In the dry process the light sensitive layer contains both the diazo compound and a coupler together with acids and various other stabilizing substances. After the treated base has been exposed to light, the print is formed by the use of hot aqueous ammonia fumes.

Each of the above systems has serious disadvantages. The principal objection to the dry process is that it requires the use of ammonia fumes. Because of the pungent and corrosive nature of the fumes it is necessary to provide special venting devices before the process can be used to any great extent. Although the moist process does not require the use of ammonia fumes it has the disadvantage that the developing solution must be mixed frequently because it is susceptible to oxidation. Furthermore, the evaporation of water from the developer causes crystallization to occur and often leaves a sticky mass on the developing machine.

Many attempts have been made toprovide practical two-component thermographic diazotype reproduction materials'which can be used in place of systems requiring developing solutions and/or alkaline vapors. Until very recently, these efforts for the most part were unsuccessful. Difficulties arose because of the dual need to prevent premature reaction between the diazo compound and the coupling component and to cause a rapid reaction between the components at the desired time. In the first heat developable systems, satisfactory shelf life was only accomplished at the expense of print quality. Stabilizing methods such as placing the coupler within a gelatin coating and dusting powdered coupler on the diazo coated paper prevented precoupling but also produced faint and Weak reproductions.

More recently, a heat developable diazotype system has been developed which is feasible from a commercial standpoint. In this system a layer containing an intimate mixture of a diazo compound, an azo coupling component, and an alkali generating compound is formed on a suitable base. A solution of the various materials is brushed or otherwise applied to the base. Following the removal of volatiles from the liquid coat, the paper, cloth, plastic, etc., is ready for photoprinting. A description of a prefered heat developable process is disclosed in a copending application Ser. No. 5,688 which was filed on Feb. 1, 1960, now abandoned. The disclosure of application Ser. No. 5,688 is incorporated in the present specification by reference.

Even though the most recent heat developable processes provide commercially acceptable results there is still much room for improvement both as to shelf life of the coated materials and as to the color density of the resultant reproduction. Additionally, the use of alkaline generating materials such as urea and the like is not fully satisfactory. The presence of the alkaline generator and the formation of alkaline fumes has certain disadvantages.

It is the principal object of the present invention to provide improved diazotype photoprinting materials and methods.

Another object of the invention is to provide heat developable diazotype photoprinting materials which do not require the use of alkaline generating compositions.

Another object of the invention is to provide heat developable diazotype photoprinting materials which have excellent shelf life characteristics.

A further object of the invention is to provide stable diazotype photoprinting materials which produce permanent prints of excellent quality.

Still another object is to provide improved diazotype photoprinting materials which can be used to produce reproductions in a simple and highly efficient manner.

Other objects will become apparent to those skilled in the art from the following detailed description of the invention.

In general, the present invention comprises the discovery of a heat developable diazotype photoprinting composition which does not require the presence of alkaline generating agents. More specifically, a series of compounds has been found which, when combined with a diazo compound, will form an azo dye rapidly when a given temperature is reached. The composition is highly stable under ordinary storage conditions. Still more specifically it has been found that the use of particular enolates as coupling compositions in heat developable diazotype systems provides highly unexpected and advantageous advantages over known systems of this type.

The coupling enolates employed in the present system preferably have the following basic structure:

wherein A is a substituted or unsubstituted divalent benzene or naphthalene radical, or a substituted or unsubstituted cyclohexylene (1,2) or decalin-ene (1,2) radical such as a C H group or C H group, X is a cation, preferably sodium or potassium, and R is an alkyl of l to 18 carbon atoms, preferably 1 to 6 carbon atoms and most preferably a methyl or ethyl group. Specific compounds containing the enolate structure include 2- carbomethoxyl-1,3-indanedione, which compound has the following structure (.i)Na+ and carbomethoxy-5,6-benzoindane1,3-dione sodium enolate, which compound has the following structure (l)Na In the above compounds the benzene or naphthalene rings can be substituted without adversely affecting the performance of the material. Specifically, the benzene or naphthalene ring can be substituted with 1 to 4 halogen atoms (especially chlorine or bromine) to form the tetrachlorobenzene compound, the 4-chlorobenzene compound, the tetrabromo compound, or the 4-bromobenzene compound.

The saturated form of the above compounds can also be used as couplers. These compounds would have the following formulas:

Both the cyclohexylene (1,2) and decalin-ene (1,2) radicals above can be unsubstituted or substituted with various substituents. As an example, the radicals can be substituted with 1 to 4 halogen atoms, especially chlorine or bromine, or the like.

Compound number 1 above is prepared by the pressure hydrogenation with a Raney nickel catalyst of sodio2- carbomethoxy-benzoindane-1,3-dione. Compound number 2 above can be prepared by the pressure hydrogenation with a Raney nickel catalyst of sodio-Z-carbomethoxybenzoindane-l,3-dione. Both of the above compounds give a red color with most diazo compounds.

In carrying out the process, a diazo compound and an enolate are dissolved or dispersed in an aqueous system. The pH of the dispersion preferably is maintained slightly on the acid side but also can be neutral. For example, a pH of 7 to 3 or slightly less is satisfactory. Most often, the pH will be from about 5.5 to 6.5. The sensitizer solution is then coated onto a support such as paper, plastic, and the like and then dried. The coating is applied by any of the conventional methods, such as a scraper bar or air knife, to form a thin film on the surface of the base. The coating is then dried in an oven to remove a substantial portion of the moisture. A moisture content of approximately 4 to 5% is satisfactory in most instances. At this point, the coated material is ready for use.

In making a reproduction, a sheet of the sensitized support is placed in sandwich relationship with a translucent original. The sandwich with the translucent original above the sensitized support is subjected to the action of ultraviolet light whereby the diazo in the copy paper is decomposed in the non-imaged area of the translucent original. The areas in the copy paper corresponding to the imaged area of the translucent original are protected from the action of the ultraviolet light and consequently the diazo compound in those areas is relatively unaffected by the action of the ultraviolet light. At this stage in the process, a pale yellow reproduction of the original is obtained on a slightly yellow background. The paper or support carrying the latent image is then subjected to the action of heat. Depending upon the nature of the particular enolate and the particular diazo compound, at a given temperature the components of the system will undergo a change to form an azo dye. A temperature in the area of from about to 250 F. is satisfactory in most instances to cause this change. Once again, depending upon the particular diazo compound, a print of a specific color will be formed. The background will now be white due to the fact that part of the coupler has been eliminated through the action of the heat. Where monosodium enolate of 2-carbomethoxy-indane-1,3-dione is used as the coupler, the heat eliminates the carbomethoxy group ring. The coupler then present in the sheet is indane-1,3-dione, which is colorless.

The outstanding characteristics of the present system lie in the fact that Z-carbomethoxy-indane-1,3-dione or corresponding enolates are themselves incapable of coupling with the diazo compound, or at best are very Weak couplers. On the other hand, indane-1,3-dione and related compounds are extremely active couplers. Consequently, excellent storage stability of the sensitized paper is possible with the subject system.

It is believed that a possible explanation of the mechanism of development lies in the fact that at the time of the preparation of the sensitizing solution the following initial salt may be formed:

+ NaOl ZnClz ONa COOCHa The particular diazo and enolate are only for illustrative purposes. The resultant product is the diazonium salt of the enolate. It is believed that the developing reaction proceeds as follows: i r J Although the above mechanism is only theoretical, it appears that the diazonium salt of the enolate is decomposed with the action of the heat giving off carbon dioxide and methyl alcohol, whereupon an intramolecular rearrangement takes place to form the azo dye. Whereas the enolate itself is unaffected by heat, the diazonium salt of the enolate is subject to decomposition and intramolecular rearrangement. As was pointed out above, a wide variety of diazo compounds can be used in the systems as well as a wide variety of enolates. It is essential, however, that the coupler have the enolate structure described previously. Nuclear substitution of the diazo as well as the N,N- dialkyl groups are not significant limitations although slightly different effects are obtained using various diazo materials. These differences are not sufliciently critical to cause significant differences in the effectiveness of the system. The diazo compounds would have one of two basic structures:

I II

R2 32 R o where R can be H, methyl, ethyl, etc. (usually up to 12 carbon atoms or more), until a limit of solubility could be reached. R could be methyl on up in the same manner as that derived for R. R and R could be hydrogen, alkoxy, the alkoxy grouping being again determined by the limitations of solubility, or methyl, ethyl, etc. (usually up to 12 carbon atoms or more), until again the limitations are imposed due to lack of solubility.

The second structure drawn would have similar characteristics for the R and R components, but would also include the heterocyclically substituted diazo compounds, such as morpholine, acylpiperazino, hexamethyleneimino, etc.

EXAMPLE 1 This example discloses the preparation of an enolate that can be used in the subject invention. In this process, 2-carbomethoxy-1,3-indane-dione sodium enolate is prepared through a double ester condensation of dimethyl phthalate with ethyl acetate under the influence of sodium. The reaction sequence is as follows:

(l)-Na+ stirring. A yellow precipitate begins to form after about one hour of reflux. The yellow precipitate will increase in consistency to a paste. After three hours, filter and press the cake to dryness, wash several times with ethyl acetate and finally with acetone. One hundred and seventyfive (175) grams of crude sodium salt is obtained.

The benzoindane compound is prepared in exactly the same manner with the same molar ratio of the dimethyl ester of naphthalene-2,3-dicarboxylic acid to ethyl acetate and sodium.

EXAMPLE 2 This example shows a second method of preparing enolates which can be used in practicing the subject invention. Into a 3-liter flask equipped with a high torque stirrer and a wide bore reflux condenser, 134 grams of sodium methylate are added to a solution of 346 ml. of dimethyl phthalate and 716 ml. of ethyl acetate. A yellow color appears at once. The material was brought to reflux with stirring and was maintained under reflux conditions with stirring for 16 hours. The material was then filtered while hot and washed several times with ethyl acetate and finally with acetone. Two hundred (200) grams of the crude sodium salt was obtained. The benzoindane compound is prepared in exactly the same manner with the same molar ratio.

The condensation of an aromatic diester, such as dimethyl phthalate and ethyl acetate may be effected using metallic sodium (dispersion), sodium methoxide or sodium hydride. The stoichiometry of the reaction requires a molar ratio of 1:121, but in practice the following ratios have been used:

Dicster Ester Base Metallic sodium 1. 0 3. 0-4. 0 1. 4 Sodium methoxide 1.0 5. 0-6. 0 l. 2 Sodium hydride 1. 0 3. 0-4. 0 1. 4

EXAMPLE 3 This example shows a typical formula containing a diazo compound and an enolate coupler.

Water .a m1

Pyrimidinedione g 5 Monosodium enolate of 2-carbomethoxy-indane-1,3-

1,3-dione 1 g 4 4-diazo-3-ethoxy-N,N-diethylaniline g .6

Polyethylene glycol (M.W. 4000 Carbowax Silica (particle size 5 to 8'0 microns-Syloid .244) g.. 1

Referred to below as DKO or diketocarbometoxy.

The above components are dissolved or dispersed using a pH of 7 to 3, preferably 5.5 to 6.5. The solution is coated on a suitable base to form a thin film and the paper is dried to lower the moisture content of the paper to a suitable level. A sandwich of the copy paper and the sensitized support are subjected to the action of ultraviolet light and heat developed.

In the above formula, pyrimidinedione is used as a solubilizer to hold the components in solution during the formation of the coated paper. The function of the polyethylene glycol is that of a mild humectant which aids in causing the coupling of reaction to take place. Silica is 7 sometimes added in order to improve the visual density of the final azoic dye. The essential components of the system, of course, are the diazo compound and the enolate. When developed, the print prepared from Formula 1 consists of a bright blue image on an essentially white background. The development takes place when the imaged paper is raised to a temperature of about 250 F.

EXAMPLE 4 The following formulations produced the indicated results when developed in the manner described above.

Formula No. 511-4 Water ml 100 Diketocarbomethoxy sodium enolate g 0.4 a-D-methyl-glucside g 10 p-Diazop-henylmorpholine fluoroborate salt g 0.6 Chloroacetic acid g 0.25 Mannitol g 1 The above formulation coated on paper has approximately a standard printing speed and yields a brown color.

Formula No. 515

Water m1. 100 Diketocarbomethoxy sodium enolate g 0.4 a-D-methyl glucoside g Solubilizer 106G (pyrimidinedione) g 5 p-Diazo N cyclohexyl-N- -cyano-ethylaniline zinc chloride salt g 0.6 Mannitol g 1 The above formulation coated on paper has approximately a standard printing speed and is roughly a magenta color when developed.

Formula No. 580

Water ml 100 Diketocarbomethoxy sodium enolate g 0.3 Solubilizer 106G (pyrimidinedione) g 5 a-D-methyl glucoside g 5 Glucono-delta-lactone g 2 4-diazo-2,5-dibutoxymorpholinobenzene zinc chloride salt g 0.6

The above formula when coated on paper had a printing speed faster than that of any commercially produced diazo paper and gave a rather pleasing red-purple color.

As was indicated above, any one of a wide variety of diazo compounds can be used in preparing the subject photoprinting paper. One of the unusual features of the invention lies in the fact that the selection of the diazo compound determines the color of the print. The diazos commonly used in conventional diazotype systems change the hue of the resultant dye to a greater degree when they are reacted with any one given coupler generator described herein than with any one given conventional developer. The following diazo compounds produced the indicated print color.

4-diazo-morpholinobenzene zinc chloride salt give a red color 4-diazo-N-methyl-N-beta-hydroxyethylaniline zinc chloride salt gives a violet color 4-diazo-N,N-diethylaniline zinc chloride saltviolet 4-diazo-3-methyl-N,N-diethylaniline zinc chloride saltmagenta 4-diazo-2-chloro-N,N-diethylaniline zinc chloride saltorange 4-diazo-2,5-diethoxy-p-methoxyphenyl mercaptobenzene zinc chloride saltred 2-diazo-S-diethylanilinobenzoic acid-purple 4-diazo-Nethyl-N-benzylaniline zinc chloride saltpurple 4-diazo-2,S-diethoxymorpholinobenzene zinc chloride saltorange-brown 8 4-diazo-N-ethyl-N-beta-hydroxyethylaniline zinc chloride saltred The present system has also exhibited novel characteristics when a plastic support such as Mylar is used rather than paper. Previous attempts to develop coatings on plas tics such as Mylar by a thermal process have not been entirely satisfactory, due to the fact that the development temperature generally was so high that considerable distortion of the plastic would occur. It was found, however, that a coating embodying the subject system and applied to Mylar could be utilized with great success.

EXAMPLE 5 In this example a carrier was prepared containing the following components:

Anhydrous ethanol cc 460 ZO-second butyrate g 260 Toluene c 150 Methylene chloride cc 130 Acetone cc 260 Plasticizer SAIB- cc 2 To cc. of the above solution was added the following components:

Monosodium enolate of 2-carbomethoxy-indane-1,3-

dione .3 4-diazo-N-benzyl-N-ethylaniline zinc chloride salt .3

This mixture was coated on a Mylar base in the usual manner. A print was prepared as described above by initial exposure step and a secondary development step. Development was effected with this system at a temperature of 250 F. The print obtained had an orange color and had some yellow background.

The Mylar coating described above was subjected to an accelerated aging test used to judge conventional Mylar as well as diazo products for a period of time three times that normally employed. Upon exposure and development following this test the material was found to be virtually unchanged.

A second sample of coated Mylar which had undergone the accelerated aging test described above was placed atop a sheet of newspaper, emulsion side down and was passed through an infrared reflex printing machine and processed at top speed. Under these conditions an extremely legible Mylar copy of the newsprint was obtained. Burning out the background area in this copy by exposure to ultraviolet light yielded a reflex copy which was permanent.

EXAMPLE 6 In this example numerous illustrative embodiments of the present system were coated on acetate film. The formulations produced satisfactory materials for use in microfilm duplication. Certain of the formulas that were tested were as follows:

Formula No. 1

Methyl Cellosolve ml 25 Acetic acid ml 1 Diketocarbomethoxy sodium enolate g 0.25 p-Diazophenylmorpholine fiuoborate salt g 0.30 Acetone ml 25 The above solution, coated on acetate, gave a red line print having satisfactory characteristics for use as a microfilm duplicating print.

Formula No. 2

The above, coated on acetate film, gave a red-violet print.

Formula No. 3

Methyl Cellosolve ml..- 25 Acetic acid ml 0.5 Diketocarbomethoxy sodium enolate g 0.25 p-Diazo-N-methyl-N,N-diethyl-aniline stannic chloride salt g- 0.30 Acetone ml 25 The above formula on acetate produced a violet print.

The following are examples of prints on acetate using the 2-carbomethoxy-5,6-benzoindane 1,3 dione sodium enolate designated as BDKC:

Formula No. 4

The above formula, coated on acetate, gave a dark blueviolet print 'with satisfactory to excellent background and shelf life.

Formula No. 5

Methyl Cellosolve ml 25 BDKC 0.25 p-Diazo n methyl-N,N-diethylaniline zinc chloride salt g 0.30 Acetone mL- 25 The above coating on acetate gave a blueline print with good background and shelf life characteristics.

Ordinarily, the molar ratio of the diazo compound to the enolate coupling component used in preparing the subject materials will be about 1:1. If it is desired, of course, either of the components could be used in excess. Molar ratios of 3:1 to 1:3 or even greater might be used in some instances.

Obviously many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A heat developable diazotype material comprising a support and a coating on said support, said coating comprising (1) a coupling diazo compound, and

(2) a coupler-generator for said diazonium salt,

said coupler-generator having the following structure:

wherein A is a divalent benzene or naphthalene radical, or a cyclohexylene (1,2) or decalin-ene (1,2) radical, wherein X is a cation, and wherein R is an alkyl of 1 to 18 carbon atoms.

2. A heat developable diazotype material comprising a support and a coating on said support, said coating comprising (1) a coupling diazo compound, and

(2) a coupler-generator for said diazonium salt,

said coupler-generator having the following structure:

wherein A is selected from the group consisting of phenylene, naphthalene, tetrachlorophenylene, 4 chlorophenylene, tetrabromophenylene, 4 bromophenylene, cyclohexylene (1,2), and decalin-ene (1,2), X is selected from the group consisting of sodium and potassium, and wherein R is an alkyl of 1 to 6 carbon atoms.

3. A heat developable diazotype material comprising a support and a coating on said support, said coating comprising (1) a diazonium salt, and

(2) a coupler-generator for said diazonium salt,

said coupler-generator being the sodium enolate of 2-carbomethoxy-1,3-indanedione.

4. A heat developable diazotype material comprising a support and a coating on said support, said coating comprising (l) a diazonium salt, and

(2) a couplerenerator for said diazonium salt,

said coupler-generator being the sodium enolate of 2-carbomethoxy-5,6-benzoindane-1,3-dione.

5. A method for graphically reproducing an original which comprises: placing an original having preferentially radiation-absorbing areas in contact with a supported layer of a visibly heat-sensitive composition, said composition comprising (1) a coupling diazo compound, and

(2) a coupler-generator component for said diazonium salt,

said coupler-generator component having the following formula:

wherein A is a divalent benzene or naphthalene radical, or a cyclohexylene (1,2) or decalin-ene (1,2) radical, wherein X is a cation, and wherein R is an alkyl of 1 to 18 carbon atoms; and irradiating said original with heat producing radiations to a temperature wherein said compound (1) and said compound (2) react to produce an azo dye and whereby the said original is visibly reproduced.

6. A process as in claim 5 wherein said coupler-generator is 2-carbomethoxy-1,3-indancdione sodium enolate.

7. A process as in claim 5 wherein said coupler-generator is 2-carbomethoxy-5,6-benzoindane-1,3-dione sodium enolate.

8. A process for reproducing an original which comprises: placing the original to be reproduced in superimposed relationship with a supported layer of a heat-sensitive composition, said composition comprising a mixture of a coupling diazo compound and a coupler-generator for said diazo compound, said coupler-generator having the following formula:

wherein A is a divalent benzene or naphthalene radical, or a cyclohexylene (1,2) or decalin-ene (1,2) radical, wherein X is a cation, and wherein R is an alkyl of 1 to 18 carbon atoms; irradiating said superimposed original with ultraviolet light to render the components of said composition incapable of producing an azo dye in the. areas not protected by said original; and thereafter heating said supported layer of said heat-sensitive composition to a temperature of between about 160 to 250 F., whereby an azo dye is formed and said original is visibly reproduced.

9. A process as in claim 8 wherein said coupler-generator is 2-carbomethoxy-1,3-indanedione sodium enolate.

10. A process as in claim 8 wherein said coupler-generator is 2-carbomethoxy 5,6 benzoindane-1,3-dione s0- dium enolate.

11. A process as in claim 8 wherein the molar ratio of diazo compound to coupler-generator is from about 1:3 to 3:1.

References Cited UNITED STATES PATENTS 3/1950 Straley 9691 2,500,099 2,915,396 12/1959 Straw 9691 5 3,140,180 7/1964 Fritz 9691 XR 3,331,689 7/1967 Soshovsky et al. 9649 FOREIGN PATENTS 514,850 11/1939 Great Britain. 10 868,715 5/1961 Great Britain. 983,665 2/ 1965 Great Britain.

NORMAN G. TORCHIN, Primary Examiner 15 C. BOWERS, Assistant Examiner US. Cl. X.R. 

